Device for temporarily blocking the re-measurement of an electric oil level measurement of a machine, particularly an internal combustion engine

ABSTRACT

A device for electrically measuring the oil level of a machine, particularly of an internal combustion engine, is connected with a device for temporarily blocking re-measurement. The device for the measurement of the oil level comprises a measurement probe (2) which is heated by a constant current during a connect time which is commenced in an automotive vehicle by a switch on a battery terminal (15). Furthermore, means are provided for comparing an initial voltage U O  of the measurement probe at the start of the connect time with a measured voltage at the end of the connect time of a measurement period in order to form a result of the comparison which corresponds to the oil level. A signalling logic (7) which signals ranges of the oil level can be controlled by said result. The blocking-time transmitter, in combination with a control logic (10) for the total program control, blocks repeated measurement during at least one predetermined period of time after the machine is turned off or again turned on. In order to take into account a temperature-dependent difference in return-flow time of the oil in ducts of the machine before a new measurement, the blocking-timer transmitter (21-24) can be controlled to produce a variable blocking time as a function of the initial voltage U O  of the initial measurement, in such a manner that the blocking time decreases with an increase in the initial voltage U O .

RELATED APPLICATION

This application is a continuation of my co-pending application Ser. No.07/139,611 filed Dec. 30, 1987 now abandoned which in turn is adivisional application of Ser. No. 06/762,939 filed Aug. 6, 1985 (nowU.S. Pat. No. 4,739,301 issued Apr. 19, 1988).

FIELD AND BACKGROUND OF THE INVENTION

The present invention relates to a device for temporarily blocking there-measurement of an electric oil-level measurement of a machine.

Particularly the invention relates to a device for temporarily blockingthe re-measurement of an electric oil measurement of a machine,particularly an internal combustion engine, it having a measurementprobe which is heated by a constant current during a connect time whichis commenced by a switch for the placing in operation of the machine, inparticular an ignition switch, means for comparing an initial voltageU_(O) on the measurement probe at the start of the connect time with ameasurement voltage at the end of the connect time of a measurementperiod, a signalling logic which can be controlled as a function of theresult of the comparison in order to signal the oil level, and ablocking-time transmitter which, in combination with a control logic,blocks repeated measurement for at least a predetermined period of timeafter the machine is turned off or again turned on.

With one such known device the oil level of an internal combustionengine is measured in the manner that upon actuation of the ignition keyand before the starting of the internal combustion engine themeasurement probe is acted on by a constant current and the voltage dropon it is measured and evaluated during different points of time of theconnect time. The measurement probe has a relatively high temperaturecoefficient, in particular a positive temperature coefficient in thecase of a measurement probe consisting of nickel/iron wire, so that thevoltage drop on the measurement probe increases with an increase in thetemperature. At the start of the connect time of the constant current, afirst measurement is effected, namely with an initial voltage U_(O)which is dependent on the ambient temperature and/or the oiltemperature. Upon the heating of the measurement probe by the constantcurrent the temperature of the measurement probe changes as a functionof the level of the oil, which takes up a larger or smaller amount ofthe heat. Thus the measurement voltage which is measured at the end ofthe connect time and compared with the initial voltage U_(O) is ameasure of the oil level. As a function of the result of the comparison,the "warning" or "non-warning" condition of a warning lamp can bebrought about via a signalling logic.

It is known that, upon the starting of an internal combustion engine andits further operation, the oil is conducted out of the crankcase sumpvia ducts to holes on the surfaces to be lubricated. As a result, theoil level in the crankcase sump drops even if a sufficient amount wasoriginally present. Upon the turning off of the engine, the oilgradually flows back into the sump, so that after a very long time anoil level is reached which is a reasonably exact measure of the amountof oil actually present.

Accordingly, the oil level which can be measured upon the starting ofthe internal combustion engine is not directly a measure of the amountof oil present in the engine, which in particular makes it difficult toeffect a properly dosed refilling of the oil. In this connection, itmust be borne in mind that, when the internal combustion engine isturned off, as a rule one does not have all the time necessary in orderto wait so as to be certain that all of the oil has returned and thusobtain a measurement result which is definitely valid. In addition tothis, there is the fact that the oil level of the internal combustionengines in automotive vehicles is frequently measured by the driver andthus not always by technically interested and/or trained persons. Ifspecial measures are not taken, it must therefore be feared that toomuch oil will be added since the signalling device erroneously signalstoo small an amount of oil in the engine, as a result of the oil whichis present in the ducts and has not flown back, or else the driver nolonger needs a warning for the reasons described and fails to refilleven if it should be necessary. The disadvantageous consequences of toosmall an amount of oil for lubrication and cooling in internalcombustion engines are well known, as are also the disadvantageousconsequences of too large an amount of oil, the excess of which, in thebest of cases, is thrown out unused by the engine.

Therefore, in one known device for the electric measurement of oil, adevice for blocking re-measurement has already been provided which isintended to take into account the return flow of the oil into thecrankcase sump. The device for blocking re-measurement has the resultthat for a fixed predetermined blocking time after an immediate restartof the engine no new measurement can, for the time being, take place inorder to permit the oil to return in the meantime.

However, it has been found that this device for blocking re-measurementcan operate satisfactorily only for given parameters of ambienttemperature and oil temperature since the viscosity, and thus the returntime of the oil, is, as is known, dependent on temperature. This has theresult that in hot weather and with a hot engine the oil flows rapidlyback into the crankcase while the same process takes a relatively verylong period of time in very cold weather and when the engine has beenoperated only for a short time.

SUMMARY OF THE INVENTION

It is an object of the present invention to improve a device fortemporarily blocking the re-measurement of an electric oil levelmeasurement of a machine in the manner that the temperature-dependentviscosity of the oil is taken into account, without therebysubstantially increasing the cost of manufacture of the device, which isintended for use also in mass-produced vehicles.

According to the invention, the blocking time transmitter (21-24) forthe production of a variable blocking time can be controlled in such amanner as a function of the initial voltage U_(O) of the initialmeasurement that the blocking time decreases with an increase in theinitial voltage U_(O) (FIG. 3).

The invention is based on the principle that the initial voltage U_(O)on the measurement probe at the start of the connect time is not onlyused to form a measurement of the oil level by comparison with themeasurement voltage measured upon the end of the connect time but also,in a second function, in order so to control the blocking timetransmitter for the production of a variable blocking time that thedifferent return-flow time of the oil, which is dependent on the oiltemperature, is taken into account before the entire device is freed foranother measurement of the oil level, for instance after refilling. Thisdevice is thus inexpensive since the initial voltage U_(O) is used forthe control of the blocking time transmitter and an electric signalcorresponding to the temperature of the oil need not be separatelyformed.

By the device of the invention the result can thus be obtained thatwithin wide range of temperatures, the oil level can within a largetemperature range only be measured again, after brief operation of amachine, so as to form a sufficiently exact signal which corresponds tothe amount of oil actually present, after the oil present in thechannels has flown back to a well-defined extent into the crankcasesump.

Such a dependence of the variable blocking time of the blocking timetransmitter on the initial voltage U_(O) or the oil temperaturecorresponding to it that the variable blocking time from 0 at 20° C.increases stepwise five minutes for every 10° K. decrease in temperaturehas been found advantageous (FIG. 3). A good approximation to the oilreturn-flow time as a function of the temperature is thus obtained withdifferent grades of oil used in internal combustion engines.

Further according to the invention, the initial voltage U_(O) can befed, via an intermediate storage (18) and an latch circuit (20), into adecoder (21) which evaluates the initial voltage U_(O) corresponding tothe characteristic curve of the variable blocking time and, for theproduction of a blocking signal, sets a counter (22) which, controlledby the control logic (10), continues to count up to a predeterminedcounting value.

This provides a particularly suitable embodiment of the variableblocking time transmitter, which is developed as a settable counter, andof the means used for its control. The control means process the initialvoltage U_(O), which in particular has been fed at the start of theconnect time of the measurement probe into an oil measurement countingmechanism for the formation of the signal analogous to the oil level.The initial voltage U_(O) is fed, via the latch circuit, into thedecoder, which contains the above-mentioned characteristic curve of thevariable blocking time as a function of the initial voltage U_(O). Thedecoder sets the counter of the blocking time transmitter, which counteris incremented with time pulses up to a predetermined final value, andduring the counting process it forms the blocking time corresponding tothe initial voltage U_(O). The output signal blocks a new measurement ofoil level via the control logic of the total program control.

Still further, in addition to the first blocking time transmitter(21-24) for the production of a variable blocking time as from theconnecting of the switch (at the battery terminal 15) for the placing inoperation again of the machine, a second blocking time transmitter (14)for the producing of a relatively short fixed blocking time as from thedisconnecting of the switch and a third blocking time transmitter (17)for the producing of a relatively long fixed blocking time as from thedisconnecting of the switch are provided, and the second or thirdblocking time transmitter is optionally activatable by the signallinglogic (7). As such, the variable blocking time transmitter which isinitiated as from the reconnecting of the switch for the placing inoperation of the machine, in particular the ignition switch, can beadvantageously combined with the second blocking time transmitter forthe production of a relatively short fixed blocking time as from thedisconnecting of the switch and with the third blocking time transmitteralso for the production of a fixed but relatively long blocking time asfrom the disconnecting of the switch. The outputs of all blocking timetransmitters are conducted, over a logical conjunction, to the controllogic of the total program control so that similar output signals blocka repetition of the measurement of the oil level. The second and thirdblocking time transmitters are not controlled as a function oftemperature but are actuated by the signalling logic only to give off,in each case, a fixed blocking time. In the event that the signallinglogic signals a "warning" operating condition, then, in particular, theblocking time transmitter of the short blocking time of preferably 30seconds is actuated. This is a minimum time of protection which isprovided for the return of the oil, but which, on the other hand, makesit possible to rapidly again measure the effect of a refilling on thelevel of the oil. If, on the other hand, it is signalled that the oillevel was in the normal range before the starting of the machine, thethird blocking time transmitter, which produces a relatively longblocking time of preferably four minutes, prevents oil being refilledprematurely after the turning off of the machine although actually asufficient amount of oil would be present after the return of the oilinto the crankcase sump. Since the above criteria, however, apply by wayof approximation only for specific pre-established temperatureconditions, the logical conjunction with the temperature-dependentformation of the blocking time provides assurance that the influence ofthe temperature-dependent oil viscosity is also taken into account.

Further according to the invention, the outputs of all blocking timetransmitters are conducted via an OR member (15) to the control logic(10), so that a new measurement is blocked as long as a blocking timesignal is present at any one of the outputs, all blocking timetransmitters acting via said OR member in the same direction on thecontrol logic to block a new measurement.

With the above and other objects in view, the present invention willbecome more clearly understood in connection with the detaileddescription of a preferred embodiment, when considered with theaccompanying drawings, of which:

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a simplified circuit diagram for the development of themeasuring device with repetition block;

FIG. 2 is a graph showing the current and voltage variations in a knownmeasurement probe in connection with the device shown in FIG. 1; and

FIG. 3 is a graph showing the dependence of the variable blocking timeon the temperature.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The measuring device with measurement repetition block according to FIG.1 refers to the measurement of the oil level of an automobile engine.For the operation of the electrical device, the battery voltage at theso-called terminal 30 and the voltage at the ignition lock at theso-called terminal 35 are used ("35" and "30" are therefore notreference numbers). The battery voltage feeds a bipolar IC 1 which,inter alia, produces the constant current of a measurement probe 2. Forthis purpose, the current is measured on a resistor 3.

The voltage drop on the probe 2 is evaluated in a logic IC which isdesignated generally as 4. The logic IC also contains the measurementrepetition block.

In detail, the logic IC contains an analog-digital converter 5 whichconverts the voltage drop on the measurement probe 2 into a digitalnumber. This number is fed into an oil measurement counter 6. On theoutput side, the oil measurement counter is connected with a signallinglogic 7 which distinguishes between the "warning" and "non-warning"conditions and sends a corresponding signal to a driver 8 outside thelogic IC for the control of a signal lamp 9.

The oil measurement counter and the lamp logic are controlled by controllogic from the total program control 10 and a clock pulse transmitter11:

Referring to FIG. 2, after the connecting of the constant current byactuation of the ignition key at terminal 35, a constant current pulseis produced as from t₀. The initial voltage U_(O) which drops then for ashort time until the time t₁, which voltage is determined upon the firstmeasurement, experiences conversion into a corresponding digital numberby the analog-digital converter 5 and is fed as such into the oilmeasurement counter 6. Then, at the end of the connect time, a secondmeasurement is effected of the voltage on the measurement probe, now themeasurement voltage, at the time t₂, which voltage is also fed into theoil measurement counter as a digital number and is compared in the oilmeasurement counter with the digital number of the initial voltageU_(O). The result of the comparison forms a measure of the oil level.Depending on the result of the comparison, which again is present as adigital number, the signalling logic recognizes the normal condition,signals "no warning," and the warning lamp remains off. Otherwise, inthe event of "warning," the warning lamp is continuously lit. Thesignalling logic may have still another function, for the detection of ashort circuit or interruption of the measurement probe, whereupon thewarning lamp lights up continuously.

The state of the signalling logic is stored via a line 12 in the controllogic 10.

The control logic 10, via a line 13, controls the so-called secondblocking time transmitter--the first blocking time transmitter will bediscussed further below--which is adapted to give off a relatively shortfixed blocking time of 30 seconds as from the disconnecting of theignition at the terminal 35. The second blocking time transmitter ismarked 14. It acts, via an OR member 15 on the control logic in themanner of a self-holder so that no new measurement of the oil level isinitiated by the control logic as long as the blocking time of 30seconds has not expired.

In similar manner, a new measurement of the oil level is interruptedwhen the signalling logic signals the "no warning" condition over theline 12. Thereupon a third blocking-time transmitter 17 is initiated viaa line 16, so that it operates for a period of 256 seconds, equal toabout 4 minutes, and gives off a self-holding signal via the OR member15 to the control logic 10, which in its turn blocks further measurementas from the disconnecting of the ignition for the said period of time.

For the variable blocking-time transmitter, a digital numbercorresponding to the initial voltage U_(O) --block 18--is read out ofthe oil measurement counter 6 and read on a pulse on a line 19 from thecontrol logic into a latch 20 and stored therein. For the first blockingtime transmitter a decoder 21 on the latch 20 converts the digitalnumber corresponding to the initial voltage U_(O) into a numericalvalue, which, in combination with a settable counter 22 which isconnected to decoder 21 and into which counter the coded digital numberis fed at a setting input 23, produces a variable blocking timecorresponding to the graph of FIG. 3.

In FIG. 3, the blocking time produced as a function of the oiltemperature in the settable counter 22 is shown, namely decreasing insteps of 5 minutes each per 10° K. so that at an ambient temperature of20° C. the variable blocking time is zero.

The counter, which is set with a coded number as a function of thenumber in accordance with the initial voltage U_(O), is decremented bytime pulses at an input 24. This is done as soon as a signal is carriedon a line 25 from the control logic upon the connecting of the ignition,which signal is brought about by the voltage at terminal 35. Thesettable counter 22, via the OR member 15, thus blocks the controllogic, which prevents another measurement for the blocking time whichcan be noted from FIG. 3, as from early reactuation of the ignition key.

With the device shown in FIG. 1, therefore, various parameters which arecontrolling for a blocking of a measurement of the oil level are sotaken into account that, on the one hand, as soon as possible after theadditional filling of a quantity of oil, it can be noted how high thelevel in the machine actually is, while, on the other hand, erroneousmeasurements due to the oil which is present in the ducts of the machineand has not yet flown back are avoided.

In the device described, the initial voltage U_(O) of the oil level rodis used to control the blocking-time transmitter.

It is evident that a different, more accurate transmitter can also beused for this, if the oil level rod is not sufficiently accurate astemperature sensor.

Furthermore, it should be pointed out, in particular, that the time ofthe variable measurement repetition block can also elapse during travel.

It is noted that the initial voltage measurement is an accurate measureof oil temperature at all values of oil level because this measurementis made before the probe has a chance to heat up from current passingthrough the probe. Therefore, the temperature of the probe is the sameas the temperature of the oil in the engine oil sump. The electricalresistance and voltage drop across the probe are determined only by theoil temperature, and are not affected by subsequent heating of theprobe, which heating is dependent on the level of oil in the sump. Anincrease in oil temperature raises or lowers the probe voltage dependingon whether the probe is fabricated of material having, respectively, apositive or negative temperature coefficient.

Legends of FIG. 1

6 Oil measurement mechanism

7 Signalling logic

8 Driver

10 Control logic

11 Clock

12 Terminal 30

13 Terminal 35

17 Self-holder 256 seconds

17a Self-holder 30 seconds

17b Settable counter

Legends of FIG. 2

a Terminal 15

b i=constant

c U_(probe)

Legends of FIG. 3

d blocking time t in minutes

I claim:
 1. In a device for temporarily blocking re-measurement of anelectric oil measurement of a machine, having a measurement probe whichis heated by a constant current during a connect time which is commencedby a switch for placing the machine in operation, means for comparing aninitial voltage on the measurement probe at a start of the connect timewith a later measurement voltage at the end of the connect time of ameasurement period, a signaling logic controllable as a function of theresult of the comparison in order to signal the oil level, and ablocking-time transmitter which, in combination with a control logic,blocks repeated measurement for at least a predetermined period of timeafter the machine is turned off or again turned on, the improvementwherein said device further compriseselectric circuit meansinterconnecting said probe with said blocking-time transmitter, saidcircuit means being driven by said control logic to transmit saidinitial voltage from said probe to said blocking-time transmitter, saidinitial voltage being a measure of temperature of the oil, there being asingle probe providing both said initial voltage and said latermeasurement voltage; and wherein said blocking-time transmitter producesa variable blocking time as a function of said initial voltage such thatthe blocking time decreases with an increase in temperature of the oil;said comparing means includes a counter, there being ananalog-to-digital converter interconnecting said counter and said probefor converting analog voltage of said probe to a digital number for saidcounter, both said initial voltage and said later measurement voltagebeing converted to digital numbers for said counter; and said counterand said signaling logic is responsive to both said initial voltage atthe start of said connect time and said later measurement voltage at theend of said connect time, under control of the combination of saidcontrol logic and said blocking-time transmitter, to output an oil-levelmeasurement.
 2. The device according to claim 1, whereinthe variableblocking time is from 0 at 20° C. and increases stepwise five minutesfor every 10° K. decrease in temperature.
 3. The device according toclaim 1, wherein said circuit means further comprisesan intermediatestorage, and a decoder; and the initial voltage is feedable, via saidintermediate storage, into said decoder which evaluates the initialvoltage corresponding to a characteristic curve of the variable blockingtime.
 4. The device according to claim 1, wherein said circuit meansfurther comprisesan intermediate storage, a latch circuit, and adecoder; and the initial voltage is feedable, via said intermediatestorage and said latch circuit, into said decoder for the production ofa blocking signal; and said blocking-time transmitter comprises acounter, wherein said blocking signal sets said counter which,controlled by said control logic, continues to count up to apredetermined counting value.
 5. The device according to claim 1,wherein said circuit means further comprisesan intermediate storage, alatch circuit, and a decoder; and the initial voltage is feedable, viasaid intermediate storage and said latch circuit, into said decoder,said decoder evaluating the initial voltage corresponding to acharacteristic curve of the variable blocking time to produce a blockingsignal; said blocking-time transmitter comprising a counter, whereinsaid blocking signal sets said counter which, controlled by said controllogic, continues to count up to a predetermined counting value.
 6. Thedevice according to claim 1, whereinsaid machine is an internalcombustion engine, and said switch is an ignition switch.